Follistatin 344
FST-344 Β· Follistatin Β· FS-344
Naturally occurring glycoprotein that acts as a potent antagonist of myostatin (GDF-8) and activin, thereby removing the primary brakes on muscle growth. The 344 isoform has reduced heparin binding and preferential systemic distribution versus the locally-acting 315 isoform.
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Mechanism of Action
Binds and neutralises myostatin and activin A with high affinity, preventing them from signalling via ActRIIB receptors. This disinhibits Akt/mTOR pathway in myocytes, allowing unconstrained protein synthesis and satellite cell activity. Concurrently reduces fat deposition via inhibition of activin-driven adipogenesis.
Clinical Applications
- βMuscle mass gain in athletes and body composition optimisation
- βSarcopenia prevention and reversal in older adults
- βMuscle wasting conditions (cachexia, chronic disease)
- βCombined with GH secretagogues for synergistic anabolic effect
Dosing Protocol
Recommended Dosing
SC injection. 100 mcg every other day for 10 days (standard research cycle), then 30β60 day break. Some protocols use 50β100 mcg/day for 5 consecutive days. Very limited human data β use minimum effective dose and extended breaks.Safety & Contraindications
Possible Side Effects
- β Excessive muscle fullness or pump (can be uncomfortable in some muscle groups)
- β Tendon stress β rapid muscle growth may outpace tendon adaptation
- β Unknown long-term safety profile in humans
- β Potential FSH suppression (activin normally stimulates FSH; blocking activin reduces FSH)
Contraindications
- βActive malignancy β myostatin inhibition may support tumour growth in some cancers
- βFertility treatment in women β FSH suppression may impair follicular development
- βExisting tendinopathy β rapid muscle growth without tendon readiness increases injury risk